1. Field of the Invention
The present invention pertains to a fusing device used in an image forming apparatus such as an electrophotographic copying machine, printer or facsimile, and more particularly, to a fusing device that fuses a toner image to a recording medium using low-frequency induction heating.
2. Description of the Related Art
An electrophotographic copying machine, printer or facsimile has a fusing device that fuses onto a sheet a toner image formed on the sheet, which comprises the recording medium. While various methods may be used by the fusing device, fusing devices using the induction heating method have been proposed in response to the recent demand for energy conservation.
For example, Japanese Laid-Open Patent application Hei 10-123862 discloses an induction heating fusing device in which a core that forms a closed magnetic circuit runs through a conducive fusing roller and a coil comprising spirally formed wire is coaxially located inside the fusing roller. In this fusing device, a magnetic flux is caused inside the core by supplying electric current to the coil, and the magnetic flux induces an inductive current in the fusing roller so that the fusing roller is heated by means of Joule heating.
Due to the direct heating of the heating member, such as the fusing roller, by means of electromagnetic induction, a fusing device using the induction heating method has higher heat conversion efficiency than the halogen lamp heating method. Consequently, the temperature of the surface of the fusing roller may be quickly increased to the fusing temperature using a smaller amount of power, thereby satisfying the demand for energy conservation. In particular, devices having a core that forms a closed magnetic circuit, as in the laid-open patent application described above, exhibits little leakage of the magnetic flux, and can efficiently induce a secondary electric current in the fusing roller, offering a high energy conservation effect. They are therefore suited for large high-speed copying machines and high-speed printers.
In the induction heating fusing device disclosed in the laid-open patent application referred to above, the core comprises a first iron core and a second iron core that is rotatably mounted to the first iron core, and the fusing roller may be mounted or removed by opening the first and second iron cores relative to each other.
Using this conventional induction heating fusing device, the fusing roller may be easily mounted or removed. However, because the mounting or removal of the fusing roller is performed by opening the first and second iron cores relative to each other, an operation that is somewhat complex for a general user must be performed. Therefore, an induction heating fusing device that allows the user to be able to replace the fusing roller more easily is desired.